1. Field of the Invention
The present invention relates to a filter bag typically for use in homogenization of food samples.
2. Description of the Prior Art
Any food sample must be subjected to microorganism inspection with an electronic microscope. Before subjected to the inspection, a filter bag containing the food sample and suitable dilution is set to a predetermined position in a homogenizer. The homogenizer has, for example, a pair of reciprocating rollers or paddles, which are driven by a drive mechanism connected to a motor to repeatedly press one side of the filter bag. Another type of the homogenizer is disclosed in Japanese patent No. 2,816,669 issued to Matsuo, which is incorporated herein for reference. Homogenization may also be carried out without using a homogenizer. In handwork homogenization, the bag containing the food sample and dilution is pressed by a hand roller or squeezed by hand. During mechanical or handwork homogenization over a sufficient period of time, the food sample contained in the filter bag is mechanically smashed and homogenized to prepare a suspension. Then, a small quantity of the suspension is pipetted to a laboratory dish which is placed on a slide glass of the electronic microscope for microorganism inspection.
A typical example of the filter bag is disclosed in Japanese utility-model publication No. 6-23280 which comprises a pair of rectangular thin plastic films sealed to each other at three edges thereof to provide an open-top interior, which is divided into two sections by a filter. The filter has substantially the same size with the opposite two plastic films and is interposed therebetween at the sealed three edges, so that the divided two interior sections has the same volume. The food sample with dilution is poured into one section which is referred to as a sample receiving section. While the food sample is smashed during homogenization, it tends to pass through the filter to enter the other section which is referred to as a suspension collection section. When the food sample is sufficiently smashed to be passed through the filter, it enters the suspension collection section. The suspended food obtained in this section may be pipetted with a Piet inserted through the open-top of the filter bag. Any particles which can not pass through the filter remain in the sample receiving section as a residue.
In this prior art filter bag, the filter is interposed integrally between the opposite two plastic films, which makes it difficult to enlarge the open-top of the filter not only when pouring the food sample and the dilution into the sample receiving section but also pipetting a small quantity of the suspended food in the suspension collection section.
The size of the filter bag depends on a type of the homogenizer but has usually 30 cm or more in length (height). Pipettes have various length. When the liquid level of the suspension collected in the suspension collection section is relatively low, which is to be pipetted with a pipette smaller than the filter bag, it may be possible that the tip end of the pipette does not reach the liquid level of the suspension. In this case, the operator is required to squeeze the bottom of the suspension collection section from opposite sides or tilt the filter bag so that the liquid level is elevated sufficiently to allow the pipette to become accessible. This is off course troublesome operation. Further, excessive squeezing or slanting operation would cause overflow of the suspension from the open-top of the filter bag, thereby soiling the operators hands and clothes.
Accordingly, it is a principal object of the present invention to overcome the drawbacks and disadvantages of the prior art filter bag.
Another object of the present invention is to provide a filter bag having an easily enlargeable open top to facilitate entry of a food sample in a sample receiving section as well as pipetting of a suspension from a suspension collection section.
In accordance with an aspect of the present invention, therefore, there is provided a filter bag comprising a first thin plastic film; a second thin plastic film having substantially the same size with the first plastic film and sealed to the first plastic film at a first side-peripheral edge, a second side-peripheral edge opposite to the first side-peripheral edge and a bottom peripheral edge thereof to provide an open-top interior, and a filter sheet having a length substantially equal to the first and second plastic films and a width smaller than the first and second plastic films. The filter sheet has a first longitudinal edge interposed and sealed together between the first side-peripheral edges of the first and second plastic films and a second longitudinal edge, opposite to the first longitudinal edge, sealed to the inside of the first plastic film at an intermediate position in width of the filter bag. The filter sheet is also sealed to the inside of the second plastic film, in vicinity to the first longitudinal edge, to provide a half-length seam extending from the open top edge halfway toward the bottom of the filter bag. A sample receiving section of a larger volume is defined between the first and second plastic films and the filter sheet whereas a suspension collection section of a smaller volume is defined between the first plastic film and the filter sheet.
In a preferred embodiment, the first plastic film includes a pull-tab near the open top edge, between the second longitudinal edge and the half-length seam. The pull-tab is manually pulled down over a given length to provide a pipette-inserting window. The pull-tab may have substantially semicircular arc or crescent.
The first plastic film may have one or plural indexes below the pull-tab at predetermined level from the bottom in relation to a quantity of the food sample to be received in the sample receiving section The indexes serves guide lines in pull-down of said pull-tab.